A fundamental principle of an eddy current retarder, being used as an automobile auxiliary braking device, is as follows: When a metal plane or a metal cambered surface is moving, eddy current is generated by induction inside the plane or surface and accordingly a braking torque is generated. The kinetic energy of the automobile is converted into thermal energy to be consumed through a medium, such as a magnetic field, and thus a retarding force can be realized. A prominent characteristic of the eddy current retarder is the non-contact brake. By improving the brake performance of the automobile, rapid loss of a brake block and a tire caused by friction in the traditional way of braking can be avoided. Moreover, the braking noise can be eliminated; the environmental pollution can be avoided; safety, comfort and economic efficiency in driving the car can be greatly improved; the fatigue of a driver can be alleviated; the working efficiency can be improved; the slamming on the brake can be reduced; and the car is smoother to drive. In addition to the advantages of the eddy current retarder the self-excited eddy current retarder is also capable of self-generating such that additional or enlarged power generator and storage battery of the automobile are unnecessary. Further, the issue of matching a retarder excitation power supply and a car-mounted power supply is eliminated.
Existing self-excited retarders generally consist of a stator with a plurality of groups of excitation coils, a rotor with air duct and a power generation system. The rotor is arranged on a transmission shaft of the automobile, and the coils of the stator are fixed on a car frame. A power generator is a three-phase power generator and supplies direct-current (DC) excitation after being rectified by a rectifier to the stator. When the power generation system is not in operation, no current flows through the coils of the stator, and the self-excited retarder stays at a non-braking state. When the power generation system is started to supply power to the retarder, the coils of the stator are electrified, and an inner plane of a housing rotates to cut magnetic induction lines, i.e., an eddy current is generated on the inner plane, so that a braking moment is generated. Accordingly, generated heat accumulates on the rotor and is dissipated into air through a heat dissipation fin on the rotor. The air-cooling way of heat dissipation has relatively low heat dissipation efficiency, is incapable of dissipating the heat quickly and effectively into the air, and is likely to cause thermal decay. Furthermore, existing retarders tend to have relatively complex structure due to multiple groups of coils. To ensure a constant clearance between the rotor and the stator, high precision in assembling the retarder is required, and the assembling is relatively troublesome. Moreover, control is relatively complicated as there are many wires extending from the coils.